Joystick Control

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Overview

This package can be used to control the movements of any X-Series robotic arm using a SONY PS3/PS4 controller or Microsoft Xbox360 controller (untested) via Bluetooth. In this demo, the ‘arm’ joints are set to work in ‘position’ control mode while the gripper operates in ‘PWM’ mode. Refer to the joystick button map below to see how to operate the robot. Specifically, some of the joystick controls manipulate individual joints while others are used to perform ‘inverse kinematics’ on all the joints to get the end-effector of the robot (defined at ‘ee_gripper_link’) to move as if it’s in Cartesian space. This is done using the modern_robotics code library offered by Northwestern University.

Structure

../_images/xsarm_joy_flowchart_ros2.png

As shown above, the interbotix_xsarm_joy package builds on top of the interbotix_xsarm_control package. To get pointers about the nodes in that package, please look at its README. The other nodes are described below:

  • joy - a ROS driver for a generic Linux joystick; it reads data from a joystick over Bluetooth and publishes sensor_msgs/msg/Joy messages to the commands/joy_raw topic
  • xsarm_joy - responsible for reading in raw sensor_msgs/msg/Joy messages from the commands/joy_raw topic and converting them into ArmJoy messages; this makes the code more readable and allows users to remap buttons very easily later.
  • xsarm_robot - responsible for reading in ArmJoy messages and sending joint and gripper commands to the xs_sdk node; while the ‘waist’ joint can be directly controlled via the PS3/PS4 joystick, other buttons allow position-ik to be performed using all the arm joints.

Usage

After pairing your Bluetooth joystick controller using the Pairing Your Controller Guide, type the following in a terminal (let’s say to control the WidowX-200 arm):

$ ros2 launch interbotix_xsarm_joy xsarm_joy.launch.py robot_model:=wx200

A red error message might appear in the screen saying Couldn't open joystick force feedback!. This is normal and will not affect the joystick operation. To further customize the launch file at run-time, look at the table below:

Argument Description Default Choices
robot_model model type of the Interbotix Arm such as wx200 or rx150.   px100, px150, rx150, rx200, wx200, wx250, wx250s, vx250, vx300, vx300s, mobile_px100, mobile_wx200, mobile_wx250s
robot_name name of the robot (typically equal to robot_model, but could be anything). LaunchConfig(robot_model)  
use_rviz launches RViz if set to true. true true, false
mode_configs the file path to the ‘mode config’ YAML file. LocalVar(‘FindPackageShare(pkg= interbotix_xsarm_joy) + ‘config’ + ‘modes.yaml’’)  
threshold value from 0 to 1 defining joystick sensitivity; a larger number means the joystick should be less sensitive. ‘0.75’  
controller type of controller. ps4 + ‘ps3’ + ‘xbox360’  
launch_driver true if xsarm_control should be launched - set to false if you would like to run your own version of this file separately. true true, false
use_sim if true, the DYNAMIXEL simulator node is run; use RViz to visualize the robot’s motion; if false, the real DYNAMIXEL driver node is run. false true, false
base_link_frame name of the ‘root’ link on the arm; typically base_link, but can be changed if attaching the arm to a mobile base that already has a base_link frame. base_link  
use_gripper if true, the default gripper is included in the robot_description parameter; if false, it is left out; set to false if not using the default gripper. true true, false
show_ar_tag if true, the AR tag mount is included in the robot_description parameter; if false, it is left out; set to true if using the AR tag mount in your project. false true, false
show_gripper_bar if true, the gripper_bar link is included in the robot_description parameter; if false, the gripper_bar and finger links are not loaded. Set to false if you have a custom gripper attachment. true true, false
show_gripper_fingers if true, the gripper fingers are included in the robot_description parameter; if false, the gripper finger links are not loaded. Set to false if you have custom gripper fingers. true true, false
use_world_frame set this to true if you would like to load a ‘world’ frame to the robot_description parameter which is located exactly at the ‘base_link’ frame of the robot; if using multiple robots or if you would like to attach the ‘base_link’ frame of the robot to a different frame, set this to false. true true, false
external_urdf_loc the file path to the custom urdf.xacro file that you would like to include in the Interbotix robot’s urdf.xacro file. ‘’  
hardware_type configures the robot_description parameter to use the actual hardware, fake hardware, or hardware simulated in Gazebo. actual actual, fake, gz_classic
robot_description URDF of the robot; this is typically generated by the xacro command. Command(FindExec(xacro) + ‘ ‘ + LocalVar(‘FindPackageShare(pkg= interbotix_xsarm_descriptions) + ‘urdf’ + LaunchConfig(robot_model)’) + ‘.urdf.xacro ‘ + ‘robot_name:=’ + LaunchConfig(robot_name) + ‘ ‘ + ‘base_link_frame:=’ + LaunchConfig(base_link_frame) + ‘ ‘ + ‘use_gripper:=’ + LaunchConfig(use_gripper) + ‘ ‘ + ‘show_ar_tag:=’ + LaunchConfig(show_ar_tag) + ‘ ‘ + ‘show_gripper_bar:=’ + LaunchConfig(show_gripper_bar) + ‘ ‘ + ‘show_gripper_fingers:=’ + LaunchConfig(show_gripper_fingers) + ‘ ‘ + ‘use_world_frame:=’ + LaunchConfig(use_world_frame) + ‘ ‘ + ‘external_urdf_loc:=’ + LaunchConfig(external_urdf_loc) + ‘ ‘ + ‘hardware_type:=’ + LaunchConfig(hardware_type) + ‘ ‘)  

To understand how the joystick buttons map to controlling the robot, look at the diagram and table below. Note that while the Xbox360 has a slightly different naming convention, the button placement is essentially the same:

../_images/ps3.jpg
Button Action
START/OPTIONS move robot arm to its Home pose
SELECT/SHARE move robot arm to its Sleep pose
R2 rotate the ‘waist’ joint clockwise
L2 rotate the ‘waist’ joint counterclockwise
Triangle increase gripper pressure in 0.125 step increments (max is 1)
X decrease gripper pressure in 0.125 step increments (min is 0)
O open gripper
Square close gripper
D-pad Up increase the control loop rate in 1 Hz step increments (max of 40)
D-pad Down decrease the control loop rate in 1 Hz step increments (min of 10)
D-pad Left coarse’ control - sets the control loop rate to a user-preset ‘fast’ rate
D-pad Right fine’ control - sets the control loop rate to a user-preset ‘slow’ rate
Right stick Up/Down increase/decrease pitch of the end-effector
Right stick Left/Right increase/decrease roll of the end-effector
R3 reverses the Right stick Left/Right control
Left stick Up/Down move the end-effector (defined at ‘ee_gripper_link’) vertically in Cartesian space
Left stick Left/Right move the end-effector (defined at ‘ee_gripper_link’) horizontally in Cartesian space
L3 reverses the Left stick Left/Right control
R1 if the arm has 6dof, this moves the end-effector in a negative direction along its own ‘y’ axis
L1 if the arm has 6dof, this moves the end-effector in a positive direction along its own ‘y’ axis
PS if torqued on, holding for 3 seconds will torque off the robot; if torqued off, tapping the button will torque on the robot